In recent years, a remote access system shown in FIG. 1 is known in which a user connects to a gateway apparatus in a home network or in an intra-company network such as a LAN (Local Area Network) so as to control apparatuses such as digital home electrical apparatuses.
For example, VPN (Virtual Private Network) is an example of a secure remote access system on the Internet. VPN is a technique for encrypting data transmitted between a user terminal (client) performing remote access and a gateway apparatus (server) receiving connection from the user terminal such that the data sent and received between the user terminal and the gateway apparatus cannot be tapped by a third party.
Conventionally, as documents on remote access, the following patent documents 1-2 and non-patent documents 1-3 are known.    [Patent document 1] Japanese Laid-Open Patent Application No. 2002-135867    [Patent document 2] Japanese Laid-Open Patent Application No. 2004-266562    [Non-patent document 1] RFC2637 PPTP (Point to Point Tunneling Protocol)    [Non-patent document 2] RFC2409 The Internet Key Exchange (IKE)    [Non-patent document 3] RFC2246 The TLS Protocol Version 1.0